Ocular Gene Therapy Core

Research Interests

The major interest of the lab is the development of adeno-associated virus gene therapy vectors for clinical applications. Our major disease targets are X-linked retinoschisis, retinitis pigmentosa and macular degeneration. We are also working extensively on several areas of vector refinement including the reduction of preexisting immunity and small-molecule regulation of transgene expression.

Research Summary

The major focus of the lab is the development of AAV-based gene therapeutics for inherited and acquired ocular diseases. The lab also provides preclinical development expertise, and AAV vector production to collaborating NEI groups interested in bringing AAV vector-based gene therapeutics to the clinic.

AAV gene therapy vectors are derived from adeno-associated viruses, a replication defective subgroup of parvovirus. The name is derived from the fact that AAV replication is restricted to cells that are coinfected with a helper virus, typically adenovirus or herpes virus. Approximately 95% of the human population becomes sero-positive for human AAVs in early childhood or in adolescence and pathology in humans or animals has never been demonstrated. AAV vectors are produced by a tissue culture-based process from viral components and are composed of an icosahedral viral protein capsid that contains a therapeutic gene bounded by noncoding viral packaging signals. The vectors do not contain or express any viral genes and do not replicate. AAV vectors are attractive as potential human therapeutics because they are able to establish stable expression of a wide variety of genes, in most post-mitotic tissues, that lasts at least a decade. Furthermore, AAV vectors have demonstrated efficacy in numerous animal models of human disease including beta-thalassemia, glioma, hemophilia A and B, Parkinson’s disease, chronic heart failure, macular degeneration, retinitis pigmentosa, and several inherited retinopathies such as Leber congenital amaurosis and X-linked retinoschisis.

Our current clinical disease targets are X-linked retinoschisis, retinitis pigmentosa, and macular degeneration. Retinoschisis is a simple recessive disease which has been relatively straight forward to complement with AAV vectors in animal models. The straight forward nature of the vector complementation, and the immune privileged status of the eye, make retinoschisis an excellent first disease application for a clinical trial using the current AAV vector technology. Our laboratory is collaborating with Dr. Sieving’s laboratory in the preclinical development. AAV vector-based therapeutics for retinitis pigmentosa and macular degeneration will most likely require the vector improvements described below.

While a promising technology, AAV vectors are still relatively rudimentary and in need refinement. The two most important areas for improvement are preexisting immunity and regulation of transgene expression. Most current clinical applications employ vectors derived from human AAVs. In immunologically nave animal models these vectors typically are not affected by preexisting humoral immunity, nor do they provoke cellular immune responses. Not surprisingly, in humans they are readily neutralized by preexisting antibodies and provoke cellular immune responses against transduced cells under certain conditions. Our laboratory is developing AAV serotypes from nonprimates that have very low preexisting immunity in humans and that also have useful cellular tropisms in the eye. We intend to bring the best of these capsids to the clinic as part of an improved AAV ocular therapeutic.

The clinical development of AAV vector-based gene therapeutics has progressed very slowly because it is not currently possible to shut off transgene expression from clinical vectors, and thereby terminate therapy, or to modulate the expression of transgene products. Because of this technical limitation, clinical development of AAV gene therapeutics has been restricted to disease applications in which there is an indisputable need for the transgene product, a very wide therapeutic window, and no requirement for regulation of transgene expression. For the most part, current clinical applications are restricted to a very small set of severe genetic diseases. Experimental treatments for the major retinal diseases such as macular degeneration and retinitis pigmentosa typically involve the pharmacological expression of potentially therapeutic proteins and do not fit this profile. Consequently, clinical development of AAV vector-based therapies for these diseases is progressing sluggishly, if at all. The development of a clinically usable gene regulation technology that would permit cessation and modulation of therapy would substantially reduce the risks of clinical experimentation with AAV vectors and would allow clinical access for promising therapeutic strategies for the major retinal diseases. Current gene regulation technologies are not viable for clinical use because they require the introduction and expression of nonhuman gene products in patients or because they employ expression-regulating small molecules that are not approved for use in humans or that have significant side effects. A major goal of our laboratory is to develop clinically viable gene regulation technologies that are not immunogenic and which employ nontoxic, approved, oral drugs.

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